Apparatus for determining the gas content of metal samples



Dec. 27, 1966 K s 3,293,902

APPARATUS FOR DETERMINING THE GAS CONTENT OF METAL SAMPLES Filed April 22, 1964 2 Sheets-Sheet 1 i j a 4 I: I: T T iiig fa TGPZ/WY}? INVENTOR.

T. KRAUS Dec. 27, 1966 APPARATUS FOR DETERMINING THE GAS CONTENT OF METAL SAMPLES Filed April 22, 1964 2 Sheets-Sheet 2 INVENTOR. 7%4/2 4: A I'dZ/J 1 VM 1 y United States Patent Office 3,2933% Patented Dec. 27, 1%66 APPARATUS FOR DETERMINING THE GAS CONTENT OF METAL SAMPLES Thaddaus Kraus, Vaduz, Liechtenstein, assignor, by mesne assignments, to Bendix Balzers Vacuum, Inc., Rochester, N.Y., a corporation of Delaware Filed Apr. 22, 1964, Ser. No. 361,765

1 Claim. (Cl. 7319) The melting furnace known as the vacuum heat extraction furnace serves for the purpose of driving out gases that have been dissolved or included in small metal samples through heating and melting them under vacuum in order to analyze them quantatively with the analysis apparatus connected to the furnace. Most often one is concerned with the determination of the oxygen, hydrogen and nitrogen content of a sample. In the known furnaces of this kind the sample is introduced into a carbon or graphite crucible which is heated by resistance or induction heating. Different samples can be introduced into the crucible one after the other by means of a known lock arrangement. A sample, which has been carefully extracted and afterwards remains in the crucible contributes no further significant amount of gas to the subsequent analysis of additional samples, but in consequence of the increase of the mass situated in the crucible and the dilution of the sample material thus produced, either the extraction time becomes unbearably long or else the accuracy of the analysis is forfeited. If one wishes to achieve good accuracy of analysis and at the same time permit rapid, sequential analyses, it is essential, according to the discovery made by the inventor, to remove the residue of the preceding analysis from the crucible before a new sample is examined. The vacuum may be broken on the furnace and the furnace opened for this purpose. One must however avoid as much as possible the loss of time in frequently opening and reevacuating. One can think of different hinged arrangements to permit the crucible contents to be emptied out after each single extraction,

nevertheless the emptying of the crucible in this manner is not possible, since the molten sample in consequence of the cooling down through the carbon or graphite frequently becomes so viscous that it will not flow out by itself even when one turns the crucible upside-down. The solution of the above problem becomes increasingly more difiicult as the accuracy desired to be achieved by the analysis apparatus connected to the furnace is increased.

The invention solves these problems in a new and unexpectedly simple manner. The process, according to the invention, for the determination of the gas content of the metal sample through melting of the same under vacuum in a crucible and analysis of the gases thus set free is characterized in that after the carrying out of the outgassing of the sample the sample residue is removed from the crucible, by means of quick rotation of the same about a vertical axis, so that a sufiicient centrifugal force is exerted on it. A new arrangement for the carrying out of this process consists of an evacuable housing, a heatable crucible arranged therein for the acceptance of the sample to be investigated, a gas collection pump connectable to the referenced housing and to this is connected a gas analysis apparatus and is characterized in that the crucible within the evacuable housing is arranged to be rotatable about a vertical axis and that a driving means is provided which after the carrying out of an analysis is capable of setting the crucible into such rapid rotation that the molten liquid sample residue will be slung out of the crucible by centrifugal force.

Melting furnaces with a crucible, which can be set into rotation, are already known for other purposes, for example rotating crucibles have already been proposed for are furnaces, in order to give the upper surface of the melt a concave form surrounding the are.

In another known melting furnace the slowly rotating motion of the melt reservoir of greater diameter serves the purpose of leading different parts of the surface of the molten surface at uniform speed under a stationary electrode for the production of an arc. According to this known proposal, a small centrifugal force from the slow rotary motion will be exerted on the slag particles swimming on the surface of the melt in order to generally accelerate them to the outer rim of the reservoir and from there to be skimmed off. In practice this method does not work out; the slag gathers not at the rim but right in the center of the rotating crucible because it possesses a smaller specific gravity than the melt.

The discharge of a melt from a crucible by centrifugal force has not up to now been known. That it is advantageous, in an analytical, melting furnace, to accomplish the removal of the fluid sample residue in this manner instead of tilting, could not be concluded from the known applications of rotating melting crucibles.

An example of the execution of the process and the apparatus according to the invention will be explained below with the aid of the accompanying sketches.

FIGURE 1 shows the complete arrangement schematically.

FIGURE 2 shows an example of the construction of the furnace part.

In FIGURE 1, numeral 1 designates the housing of the vacuum furnace, 2 the crucible, 3 a formed electrical resistance heating element with the connecting current leads 4- and 5. Numeral 6 designates a rotatable shaft, which is led in a vacuum tight manner through the bottom 7 of the furnace housing, and can be driven from the outside by the motor 8. Instead of using a vacuum tight lead-through a driving means can be provided within the furnace housing, although motors in the vacuum space are undesirable on account of their out-gassing. The problem of setting a body into rapid rotation in high vacuum has already been technically solved with known rotation arrangements in X-ray tubes, and all of these referenced methods can be used here.

The furnace housing is connected by a pipe to a high vacuum pumping system consisting in the usual way of a diffusion pump 10, and a forepump Ill, Samples can be introduced into the furnace through the connection 12 by means of the lock valve 13 and the funnel 14 while the furnace remains under vacuum. The analytical apparatus for the investigation of the extracted gases may be of any desired type and is designated 15 in total. As is usual the evacuation pump is used at the same time as a collection pump for gathering the gases to be analyzed, and to whose exhaust the analyzing apparatus is connected.

An analysis is carried out in the usual manner, in which the sample is placed in the crucible where it is heated to a suitable temperature for a specified length of time, and the gases given up are collected by the pump and the analysis is performed. For the carrying out of the next analysis, the viscous residue still remaining in the crucible from the preceding analysis is flung out by the rapid rotation of the crucible so that it can no longer disturb the following analysis. A complete removal of the sam le residue is not necessary, many times a small amount of the out gassed melt from the previous sample can serve in a known manner as a premelt for the following sample.

The rotational velocity, which is great enough that the material situated in the crucible experiences an acceleration of about 10 times the acceleration of gravity is easy to attain: The centrifugal force acting on a body moving in a circle is known to be equal to MRW (where M is the mass, R the radius, W the angular velocity of the body concerned). The acceleration b is also equal to RW At a distance from the center of a mass element in the melting crucible of only 0.1 cm. and a ro tation rate f=50/sec., the acceleration already becomes 0.1(21r50) =10,0O0 cm./sec. which corresponds to approximately g (1r=3.l4, g=981 cm./sec. Under this acceleration the molten sample experience a sufficient centrifugal force, so that, in spite of its viscosity, it is reliably thrown out of the crucible.

FIGURE 2 shows a practically tested construction, in which 21 designates the furnace housing, 22 the crucible here illustrated as a cylindrical rotation body and on its upper end is shown a depression 23 to accept the sample. The rotatable body or crucible 22 is carried on a liquid cooled shaft 24. The cooling medium first enters through the conductor 25 into the annular chamber 30 formed by the lip seals 27 and 28 and by the wall of the bearing and seal housing, passing from there to the interior of the hollow shaft through the opening 31, flows as indicated by the arrow, upward in the space between the wall of the hollow shaft and the tube 32 arranged within it, entering at the upper end of tube 32, flows down again, arriving through the openings 33 and 34 in the chamber 36 formed by the seals 27 and 35 and flows out from there through the pipe 26.

The shaft is carried on the ball bearings 37 and 38, and is sealed through the additional seals 39 and 40. It projects through the bottom 41 of the furnace housing and can be driven by means of 42 with a motor from the outside.

The furnace housing is made in two parts for the purpose of easy demountability, the lower part carries the above described arrangement and is designated 21a.

The conductors 43 and 44 are carried through the bottom 41 and scaled vacuum tight once again by 45 and 46 and possess connection clamps for the heating arrangement 47 on their upper ends. This consists, in the example of construction, of a cylindrical sleeve, an electric resistance heating element surrounding the rotating body 22 of graphite or carbon (the heating body is provided with slits in a known manner in order to form a meandering extended current path). The heating element 47 heats the body 22 through radiation and is surrounded outwardly by a reflector 48 for protection against radiation losses. Those parts of the wall 49 and 50 can for example be made of high melting metals or of graphite or carbon. The upper part of the furnace housing is also built to be coolable, with cooling means connections 51 and 52 and the hollow space 53 in the wall of the housing through which the cooling medium flows.

The furnace has a vacuum connection 54 and on its upper end a provision for connecting to a lock for introducing the sample or sample storage container. The funnel shaped opening, through which the sample may be introduced is designated as 55.

Since the sample residue can be removed from the crucible after each separate analysis, the invention makes possible the use of sintered crucibles for successive analyses. Up to this time this type of crucible could only be used for the investigation of single special samples, because sintered crucibles of larger diameters are ditficult to obtain and are very expensive. Carbon free sintered crucibles have the advantage of a longer useful life, because destruction of the crucible wall through the absorption of carbon in the melt, as continuously occurs in the case of graphite or carbon crucibles, can be avoided.

I claim:

Apparatus for determining the gas content of metal samples comprising: a housing, pump means connected to said housing for evacuating said housing, gas analysis means connected to said pump means, a vertical drive shaft in said housing, a crucible in said housing mounted on said shaft for rotation about the vertical axis of said crucible, said crucible having an open depression formed therein for receiving a metal sample, mean for introducing a metal sample into said crucible, a cylindrical heating element concentric with said crucible for heating said metal sample to a viscous condition releasing gases contained therein, and means for selectively driving said shaft at a predetermined speed whereby said crucible will be rotated at a sutficiently high speed to cause sample residue to be removed from said crucible by centrifugal force.

References Cited by the Examiner UNITED STATES PATENTS 2,795,132 6/1957 Boehme et al 73-19 3,226,257 12/1965 Steele et al 210-369 X RICHARD C. QUEISSER, Primary Examiner.

JULIUS FISHER, Assistant Examiner. 

